Cassini Watch: Stormy Saturn

Right now all eyes are on Saturn’s giant moon, Titan, but the ringed planet has been putting on a show of its own: massive thunderstorms, equatorial gales, and rippling clouds. Cassini is finding Saturn’s climate more Earth-like and changeable than anyone imagined.

One breakthrough occurred when atmospheric scientist Anthony Delgenio of NASA’s Goddard Institute for Space Studies noticed that storms coincided with electrostatic discharges. That means Saturn’s stormy atmosphere is spawning potent lightning. “Saturn apparently has thunderstorms just like on Earth, except maybe the altitude is different,” Delgenio says. The observed storm systems are about 30 miles deep, three times as large as those in Earth’s much shallower atmosphere.

Cassini has also turned up signs of big shifts in Saturn’s climate. Observations by the Voyager spacecraft in the 1980s clocked winds at Saturn’s equator at more than 1,000 miles per hour. The new measurements show equatorial winds have slowed to a much more Earth-like 230 to 450 miles per hour. Delgenio is confident that both observations are correct, but he has no explanation for why conditions changed so much over the last 20 or so years.

Despite these mysterious differences, Saturn displays many weather patterns that look surprisingly like Earth’s. One Cassini snapshot shows wavy swirls between two cloud zones, probably caused by the same stirring process that can produce choppy air in clear skies during an airplane flight. Other images capture dark, hurricane-type storms and a high-altitude blue shimmer not unlike the familiar sheen of our own skies.